The objective of this research proposal is to investigate the thermoregulatory response of the chuckwalla, Sauromalus obesus, living in its natura environment, to bacterial infection. I am asking the question "what affect does the febrile response have on the thermoregulatory behavior of a desert dwelling lizard which must contend with all of the biotic and abiotic complexities of the natural environment". Fever responses have been demonstrated in a number of ectothermic vertebrates under laboratory conditions but the fever response has never been investigated in the natural environment. The physiological response of an animal maintained under laboratory conditions is not always the same as it would be under natural environmental conditions. Any treatment of a physiological disturbance should be based upon the best available information and in the case of the fever response, data gathered on animals inhabiting natural environment is preferable to information gather solely on laboratory animals. The research proposed in this grant application is significant because it represents the first attempt to gather data on the fever response by an animal in its natural environment. The chuckwalla has been selected as the experimental animal because it is the largest diurnally active reptile native to California. The large size of the chuckwalla will allow the use of temperature telemeter transmitters with a range of over 0.5 miles. Therefore, body temperature data can be gathered without disturbing the animal's normal behavior pattern. The gram-negative bacterium Aeromonas hydrophila has been used in most studies concerning fever responses of ectothermic organisms and therefore, will be used in this study. Heat killed Aeromonas will be used at a dosage of 4 x 10-9 organisms. A fever will develop within 3 to 4 hours after injection and the fever should last for 2 days. The body temperature and behavior (basking, feeding-movement, crevise seeking) patterns of control, saline injected, and bacterially injected animals will be compared.